Why not 7 or not 2 or not 5?

Question

Why 4?
https://code.sololearn.com/WZE7v2PVnSXH/?ref=app
I do not understand that code...

Answer 1

Yes size of new argument list is returned.

Answer 2

It print the size of the array after push the 7
[2,4,5,7]

Answer 3

Since you pushed 7... So final Size is displayed

Answer 4

But why it returns the size, not array?????
Without push it display array.

Answer 5

https://www.w3schools.com/jsref/jsref_push.asp

Answer 6

Why without push it returns array
But with push ut returns length?